Roof/ Shell prints mid air on Infill

[LuckStar55 0]

Hi,

 

the following is a Problem i've encountered many times....When a first roof Layer begins, Cura sets the start mid air between the Infill structure.

 

I've also included a picture. You can see that the print would not work, since the roof has nothing to stick on to.

 

Plis help😅 (this is my first time writing in a forum btw...so excited)

 

[stitch3210 2]

I just searched the forum for this problem and this almost 2 year old post here is the only thread I found.

And I'm surprised, not to see any reply.

 

I assume, this is happening to everyone and a lot of the time, but mostly goes unnoticed, because you never see it on a finished print.

The problem is, that it causes stability issues. (sorry, didn't mean to yell, my inner eye showed me people saying "so what" and moving on after reading "you never see it" 🙂)

 

See my example below.

The circle on the left starts in the air over "not-infill" (I checked, the rounded rectangle on the right also had the issue). Of course the overhanging bit will drop down and when the circle finally comes to a close, the last bit will also have nothing to hang on to´and will dangle into the hole.

This continues with the actual top fill pattern, the ends will drop where they expect to meet the wall, which just isn't there and when the layer is finished, you're left with a gaping hole.

 

I think, it took until the third or fourth layer, for that hole to finally close in my example - so eventually, you get a print, that visually looks fine on the outside. But there is an area half the size of a fingernail, that is only 1 or 2 layers thick (a flimsy 0.4 mm).

Again: you usually will not notice, unless you, like me, happen to watch at the right moment.

 

I assume, Cura is too focused on where to set the seam in this scenario. But whenever it would start right on top of infill, it should first check, if there is something more solid to start from (if there is a top surface below on the planned track) or else try starting right on an infill line.

 

Both the OP and me seem to have the cubic infill in common - just in case this is a bug limited to that type of infill. But I doubt that.

 

 

 

[MariMakes 198]

Hey @stitch3210,

 

Welcome to the Ultimaker Community 🎉

 

I recognize your issue and I believe it can be solved with a setting.
We introduced Skin Edge Support Layers to resolve this issue. 
You can read more about it here.

If you increase the setting your infill will look like this instead:


It's not enabled by default yet for all printers, that's why it might not show up for you. 

[stitch3210 2]

Interesting.

Thanks for the info!

[stitch3210 2]

Hmm. Haven't tried to actually print that, yet, but from what I can see in Cura, this just moves the problem down one layer.

The support infill is printed the same way (into mid air) and even starts at exactly the same spot (if it wouldn't, there would be a chance for the skin to start over non-affected infill).

[MariMakes 198]

In my experience, the initial material deposited mid air will not be structurally sound.
But the layers on top of that will be, just like a failed support restoring itself.
That's why I recommend the Skin Edge Support Layers for 4 layers or more.

Can you start a printjob with it and let me know if it works for you? 

[stitch3210 2]

I will definitely test it, as soon as I have enough time to monitor closely.

I will report back. Thank you!

[stitch3210 2]

Ok, I ran it with the support layers - I missed the moment, though, didn't see what was happening, but it's an improvement. There still was a hole, but much smaller, so it helps.

 

But I think the transition from infill to top layers is always going to be a bit problematic.

Rectangles or any polygon with corners will always have some corners hanging over empty space.

To fix that, the algorithm would have to be a bit more sophiticated (have the infill pattern gradually morph to provide support for the shape of the top layer).

Maybe someday someone considers that an intriguing challenge.

 

After all - the tree supports are also quite a feat. (I love them and they are the only real way for the 99% of us single-extruder users to have removable supports).

 

All in all Cura is a really superb piece of software.

[MariMakes 198]

Hey @stitch3210,

 

Thanks for getting back to us.
Have you considered using Ligthning Infill?
That might also suit your needs.